Bicycle crank arm and insert therefore

ABSTRACT

A crank arm for a bicycle may include a body extending along a body axis and having a first body end and a second body end axially spaced apart from the first body end. The insert may also include an insert provided toward the first body end. The insert may include a base portion having a radially outer surface. At least one extension may extend outwardly from the radially outer surface and may be encased within a corresponding recess in the body whereby relative planar movement between the body and the at least one extension in a first plane. The retaining portion may have a retaining portion width measured in the first direction and the retaining width may be greater than the throat width thereby inhibiting relative radial movement between the at least one extension and the recess and preventing radial extraction of the extension from the corresponding recess.

RELATED APPLICATIONS

This application is filed in accordance with 37 CFR 1.53(b) and is acontinuation of co-pending U.S. patent application Ser. No. 13/675,304filed Nov. 13, 2012, which itself is a continuation-in-part of U.S.patent application Ser. No. 12/432,681, filed Apr. 29, 2009, and both ofthese applications are hereby incorporated herein in their entirety byreference.

FIELD

The present invention relates to bicycle components such as crank armsand methods for making bicycle components.

BACKGROUND

US Patent Publication No. 2005/0199092 (Feltrin et al.) discloses aninsert for a bicycle pedal crank that is made from unidirectionalstructural fibers incorporated in a polymeric material and coupledaccording to two distinct directions. The insert has a connectionportion to connect to a part of the bicycle and a fastening portion tofasten the insert to the body of the crank arm.

SUMMARY

This summary is intended to introduce the reader to the more detaileddescription that follows and not to limit or define any claimed or asyet unclaimed invention. One or more inventions may reside in anycombination or sub-combination of the elements or process stepsdisclosed in any part of this document including its claims and figures.

Known techniques for securing an insert within a body of a crank armformed from a dissimilar material have generally failed to provide asatisfactory crank arm. In instances where the insert is formed from amaterial having a different co-efficient of thermal expansion, thermalshrinkage of the insert (for example when the crank arm is cooled toroom temperature after being formed at a relatively high temperature)tends to loosen the connection between the insert and the body as theinsert shrinks more than the body. This can lead to relative movementbetween the insert and the body when the crank arm is in use. Suchrelative movement may be undesirable as it may reduce pedalingefficiency, promote or accelerate wear of the body or insert and/or leadto the insert falling out or otherwise becoming separated from the body.

According to one broad embodiment of the teachings described herein, acrank arm for a bicycle may include a body extending along a body axisand having a first body end and a second body end axially spaced apartfrom the first body end. An insert may be provided toward the first bodyend. The insert may extend along an insert axis, define a radialdirection orthogonal to the insert axis and include a base portion. Thebase portion may have a radially outer surface surrounding an axiallyextending aperture extending through the base portion. The aperture maybe configured to receive a fastener for connecting the crank arm toanother component of the bicycle. At least one extension may extendoutwardly from the radially outer surface. The at least one extensionmay be encased within a corresponding recess in the body, wherebyrelative planar movement between the body and the at least one extensionin a first plane orthogonal to the radial direction is restrained. Theat least one extension may include a neck adjacent the radially outersurface and a retaining portion spaced radially outward from the neck.The neck may extend through a throat region of the corresponding recessand having a neck width measured in a first direction parallel to thefirst plane. The throat region may have a throat width measured in thefirst direction. The retaining portion may have a retaining widthmeasured in the first direction and the retaining width may be greaterthan the throat width thereby inhibiting relative radial movementbetween the at least one extension and the recess and preventing radialextraction of the at least one extension from the corresponding recess.

The body may be formed from a body material having a first coefficientof thermal expansion and the insert is formed from an insert materialhaving a second coefficient of thermal expansion. The second coefficientof thermal expansion may be greater than the first coefficient ofthermal expansion. Shrinkage of the insert relative to the body cannotradially extract the at least one extension from the cavity.

The extension may also include opposing first and second extensionsidewalls spaced apart from each other in the first direction. Eachextension sidewall may extend between the neck and the retainingportion. The first sidewall may be generally planar and may be inclinedat a first angle relative to the radial direction so that the extensiongenerally narrows from the retaining portion to the neck end therebywedging the extension within the recess to inhibit relative radialmovement therebetween.

The recess may include a generally planar first recess wall inclined atthe first angle relative to the radial direction. The first extensionsidewall opposing and bearing against the first recess wall wherebyshrinkage of the insert relative to the body increases the magnitude ofa first engagement force exerted between the first extension sidewalland the first recess wall thereby wedging the at least one extensionmore tightly within the recess in the first direction.

The second extension sidewall may be generally planar and may beinclined at a second angle relative to the radial direction, the firstand second extension sidewall being convergent toward the neck of theextension.

The first angle may be generally equal in magnitude to the second angle.

The recess may include a generally planar second recess wall inclined atthe second angle relative to the radial direction. The second extensionsidewall opposing and bearing against the second recess wall wherebyshrinkage of the insert relative to the body increases the magnitude ofa second engagement force exerted between the second extension sidewalland the second recess wall.

The neck has a neck depth measured in a second direction parallel to theinsert axis. The retaining portion may have a retaining depth measuredin the second direction and the throat may have a throat depth measuredin the second direction. The throat depth may be equal to or greaterthan the neck depth and may be less than the retaining depth.

The extension may also include a third extension sidewall wall generallybounded by the first extension sidewall, the second extension sidewall,the retaining portion and the neck. The third extension sidewall may begenerally planar and inclined at a third angle relative to the radialdirection so that the extension is generally tapered in the seconddirection between the retaining portion and the neck.

The recess may include a generally planar third recess wall inclined atthe third angle relative to the radial direction. The third extensionsidewall opposing and bearing against the third recess wall wherebyshrinkage of the insert relative to the body increases the magnitude ofa third engagement force exerted between the third extension sidewalland the third recess wall thereby wedging the at least one extensionmore tightly within the recess in the second direction.

The extension may also include a fourth extension sidewall spaced apartfrom the third extension sidewall in the second direction and generallybounded by the first and second extension sidewalls, the retainingportion and the neck, the fourth extension sidewall and the thirdextension sidewall being generally convergent toward the neck of theextension.

The fourth sidewall may be generally planar and extends in the radialdirection.

The at least one extension may include a first plurality of extensionscircumferentially spaced apart from each other around a circumference ofthe radially outer surface of the insert.

A second plurality of extensions may be circumferentially spaced apartfrom each other around the circumference of the radially outer surfaceof the insert and axially spaced apart from the first plurality ofextensions along the insert axis.

Each extension in the second plurality of extensions may be generallyopposite a corresponding one of the extensions in the first plurality ofextensions and may be spaced apart from the corresponding one of theextensions in the first plurality of extensions in the second direction.

The fourth extension side wall of each extension in the first pluralityof extension may be opposite the fourth extension side wall of onecorresponding extension in the second plurality of extensions.

The retaining portion may form the radially outermost portion of theextension.

A second insert may be provided toward the second body end. The secondinsert may extend along a second insert axis and may define a secondradial direction orthogonal to the second insert axis. The second insertmay include a second base portion having a second radially outer surfaceand at least one second extension extending outwardly from the secondradially outer surface. The at least one second extension may be encasedwithin a corresponding second recess in the body, whereby relativeplanar movement between the body and the at least one second extensionin a second plane orthogonal to the second radial direction isrestrained.

The at least one second extension may include a second neck adjacent thesecond radially outer surface and a second retaining portion spacedradially outward from the second neck. The second neck may extendthrough a second throat region of the corresponding second recess andmay have a second neck width measured in a fifth direction parallel tothe second plane. The retaining portion may have a second retainingwidth measured in the fifth direction and the second retaining widthbeing greater than the second neck width thereby preventing radialextraction of the at least one second extension from the correspondingsecond recess.

According to another broad aspect of the teachings described herein, acrank arm for a bicycle may include a body having comprising a first endand a second end axially spaced apart from the first end along a bodyaxis. An insert may be positioned within the body toward the first end.The insert may extend along an insert axis, define a radial directionorthogonal to the insert axis and have a radially outer surface. Theinsert may comprise a base portion having a radially outer surface and aplurality of extensions extending outwardly from the radially outersurface. Each extension may be encased within a corresponding recess inthe body, whereby relative planar movement between the body and eachextension in a first plane orthogonal to the radial direction isrestrained. Each extension may comprise a neck adjacent the radiallyouter surface and a retaining portion spaced radially outward from theneck. Each neck may extend through a throat region of one correspondingrecess and may have a neck cross-sectional area measured in a secondplane orthogonal to the radial direction. The throat may have a throatcross-sectional area measured in the second plane and the retainingportion may have a retaining cross-sectional area measured in thirdplane parallel to the second plane. The retaining cross-sectional areamay be greater than the neck portion cross-sectional area and the throatcross-sectional area thereby preventing radial extraction of eachextension from the one corresponding recess.

The body may be formed from a body material having a first coefficientof thermal expansion and the insert is formed from an insert materialhaving a second coefficient of thermal expansion, the second coefficientof thermal expansion being different than the first coefficient ofthermal expansion and shrinkage of the insert relative to the bodyincreases the magnitude of a retention force exerted between the bodyand the retaining portion of each insert.

A method of forming a crank arm during the moulding process is provided,including the steps of: a) providing an insert made of a material, theinsert defining an aperture, the insert having a plurality ofextensions, each of the extensions fitting within a correspondingrecess, wherein the neck of the insertions is narrower than a distancebetween a first side of the insertion and a second side of theinsertion; b) heating the crank arm whereby composite material curesaround the extensions, thereby defining a crank arm having a body madeof the composite material, the body defining a plurality of recesses,each of the recesses having an opening, and at least one of the recesseshaving a width from a first side of the recess to a second side of therecess exceeding the length of the opening; c) cooling the crank arm,whereby the material shrinks relative to the composite material duringcooling of the crank arm.

DRAWINGS

The following figures set forth embodiments of the invention in whichlike reference numerals denote like parts. Embodiments of the inventionare illustrated by way of example and not by way of limitation in theaccompanying figures.

FIG. 1 is a perspective view of a crank arm;

FIG. 2 is a perspective view of an example of an insert for the crankarm of FIG. 1;

FIG. 3 is a cross-sectional view of the insert of FIG. 2, taken alongline 3-3;

FIG. 4 is a cross-sectional view of the insert of FIG. 2, taken alongline 4-4;

FIG. 5 is cross-sectional view of a portion of the crank arm of FIG. 1,taken along line 5-5;

FIG. 6 is an enlarged view of a portion of the cross-sectional view ofFIG. 5;

FIG. 7 is a cross-sectional view of a portion of the crank arm of FIG.1, taken along line 7-7;

FIG. 8 is the cross-sectional view of FIG. 5 before shrinkage of theinsert;

FIG. 9 is an enlarged view of a portion of the cross-sectional view ofFIG. 8;

FIG. 10 is the cross-sectional view of FIG. 7 before shrinkage of theinsert.

DETAILED DESCRIPTION

Various apparatuses or processes will be described below to provide anexample of an embodiment of each claimed invention. No embodimentdescribed below limits any claimed invention and any claimed inventionmay cover processes or apparatuses that differ from those describedbelow. The claimed inventions are not limited to apparatuses orprocesses having all of the features of any one apparatus or processdescribed below or to features common to multiple or all of theapparatuses described below. It is possible that an apparatus or processdescribed below is not an embodiment of any claimed invention. Anyinvention disclosed in an apparatus or process described below that isnot claimed in this document may be the subject matter of anotherprotective instrument, for example, a continuing patent application, andthe applicants, inventors or owners do not intend to abandon, disclaimor dedicate to the public any such invention by its disclosure in thisdocument.

Bicycle crank arms typically form part of the crankset or chainset of abicycle. The crank arms generally extend between the bottom bracket onthe bicycle frame and the pedals. A conventional pedal bicycle has twocrank arms, typically mounted 180 degrees out of phase from each other.Crank arms can be made from any suitable material having the requiredstrength to transfer pedaling force from the user's legs to thecrankset. For example, known crank arms have been made from metals, suchas steel and aluminium, and composite materials, such as carbon fibreand other materials.

The apparatus and system according to the invention uses a series ofwidening recesses within a crank arm to mechanically lock an insert tothe carbon fibre during the cooling that takes place after the mouldingprocess. As the insert shrinks it follows the recess wall of the hollowmade by the insert rather than shrinking away from it. The insert anglecan be chosen to be equal to, greater than or less than the angle ofshrinkage at any particular location of the insert. Changing the anglechanges the gap (or interference) produced during the shrinkage therebychanging the locking characteristics and allowing the crank arm to beoptimized for a given loading.

Crank arms can be connected to the bottom bracket and/or pedals usingspindles, bolts, pins or other suitable rotatable connection mechanism.Some composite materials used to form crank arms are not well suited toconnect to or support a rotatable connection mechanism. For example,crank arms formed from carbon fibre may be relatively strong andlightweight, but the carbon fibre material may not have sufficientmechanical properties to withstand the loading and stress concentrationsexerted by the rotatable connection mechanism.

One technique to help address this problem is to manufacture a crank armhaving a body that is formed from a composite material and to provideone or more inserts at the ends of the crank arm where it is connectedto the pedal or bottom bracket. Such inserts may be formed from adifferent material than the body of the crank arm. For example, theinsert material may be selected to have sufficient strength and othermaterial properties to support the rotatable connection mechanism,including, for example, aluminum, titanium, steel, magnesium, stainlesssteel, or various plastics such as polyurethane, polypropylene, orpolycarbonate. Using the combination of a composite body and metalinsert may allow the crank arm to generally benefit from the desirableproperties of the composite material (e.g. strength, low weight, etc.)while still having sufficient connection strength.

In crank arms of this configuration, the quality of the connectionbetween the insert and the body of the crank arm can affect the qualityand/or durability of the assembled crank arm. Typically, the insertmaterial will have a larger co-efficient of thermal expansion than thecomposite body material, which can result in shrinkage of the insertrelative to the body, for example when the crank arm is cooled after thecomposite material molding process. Such shrinkage can lead to aloosening of the insert within the body. Loosening of the insert canlead to rattling, unwanted rotation of the insert relative to the body,fatigue of the body portion and ultimately failure of the crank arm. Theteachings herein describe an example of a connection between an insertand crank arm body that may help mitigate and/or eliminate loosening ofthe insert caused by differential thermal expansion.

Referring to FIG. 1, one example of a crank arm 100 includes a body 102a first insert 104 and a second insert 106. Optionally, while currentlyillustrated with two inserts 104, 106, a crank arm 100 may be configuredto include a different number of inserts, including, for example, onlyone insert.

In the illustrated example, the body 102 is generally elongate andextends along a body axis 108 between a first end 110, for connecting tobottom bracket of a bicycle, and a second end 112, for connecting to apedal assembly.

The body 102 is formed from a body material, and the inserts 104 and 106are formed from an insert material, which can be different than the bodymaterial. In the illustrated example, the body 102 is formed from carbonfiber and the inserts 104, 106 are formed from aluminium. Alternatively,the body 102 may be formed from any other suitable material, including,for example, composite materials such as fiberglass, Kevlar®, boronfiber or beryllium fiber, or metal or plastic. The inserts 104, 106 maybe formed from any suitable material that has the desired strength tosupport the rotatable connection between the crank arm and other bicyclecomponents including, for example, steel, titanium, other metals and/orplastics.

The inserts 104, 106 are configured to be mounted within the body 102,and to facilitate connection with the bottom bracket and pedal assembly,respectively. Each insert 104, 106 includes a central bore or aperture114 and 116 that is configured to accommodate a fastener. The bores 114and 116 may be threaded or otherwise configured to mate with acorresponding fastener. In the illustrated example, both inserts 104 and106 extend along respective insert axes 118 and 120. The inserts 104,106 in the crank arm 100 can be identical, or may be different from eachother. Providing differently configured inserts may help facilitatedifferent types of connections between the crank arm 100 and the bottombracket and pedal assembly. For simplicity, insert 106 will be describedin greater detail herein, but it is understood that insert 104 caninclude identical and/or analogous features.

Referring to FIG. 2, insert 106 includes a generally cylindrical bodyportion 112 surrounding the bore 116 and having a radially outer surface124 (see FIG. 3). To help secure the insert 106 within the body 102, theinsert 106 can include one or more anchor members 125 that areconfigured to be embedded in and encased by the body 102. The anchormembers 125 can be configured to help inhibit rotation of the insert 106relative to the body 102 about the insert axis 120, and/or to helpinhibit translation of the insert 106 relative to the body 102 along theinsert axis 120.

In the illustrated example, the anchor members 125 include a pluralityof extensions 126 extending generally outwardly from the radially outersurface 124 (see FIG. 3) of the insert 106. The extensions 126 include afirst set of extensions 126 a that are circumferentially spaced apartfrom each other about the periphery or circumference of the insert 106by a first spacing distance 128 (illustrated as a centre-to-centredistance), and are arranged to provide a first ring of extensions 130(see FIG. 5). The first ring of extensions 130 is axially positionedtoward a first end 132 of the insert 106.

The extensions 126 also include a second set of extensions 126 b thatare circumferentially spaced apart from each other about the peripheryof the insert 106 by a second spacing distance 134, and are arranged toprovide a second ring of extensions 136 (see FIG. 4). Referring to FIG.4, the second ring of extensions 136 is axially positioned toward asecond end 138 of the insert 106 and is axially spaced apart from thefirst ring of extensions by a ring spacing distance 140.

In the illustrated example, each extension 126 a in the first ring 130is circumferentially aligned with an opposing extension 126 b in thesecond ring 136. In this configuration, axial gaps 142 are providedbetween opposing extensions 126 a and 126 b. Arranging the extensions126 a and 126 b in this pattern may help simplify the manufacturing ofthe insert 106. Alternatively, the extensions 126 a and 126 b may beconfigured so that extensions 126 a in the first ring 130 arecircumferentially offset from extensions 126 b in the second ring 136.While illustrated with 10 extensions in each of the first and secondrings, the insert may be provided with any suitable number ofextensions, including, for example, between about 1 and about 40extensions or more, and preferably between about 4 and about 30extensions.

Referring to FIG. 3, each extension 126 a extends outwardly from a neckportion 144 adjacent the radially outer surface 124 of the insert 106and distal end or tip 146 that is radially outboard from the neckportion 144 in the radial direction 148. The tip 146 includes a radiallyoutwardly facing end face 150. In the illustrated example, eachextension includes four, generally planar sidewalls 152, 154, 156 and158 (FIG. 4) that extend between the neck 144 and the tip 146.Alternatively, the extensions 126 may be of any other suitable shape,including, for example, spherical, conical, pyramidal and other shapesthat can be configured to function as described herein.

Referring to FIG. 3, the neck portion 144 defines a neck width 160,measured in a plane 162 that is orthogonal to the radial direction 148,and, referring to FIG. 4, a neck depth 164, measured in the axialdirection. The neck width 160 and neck depth 164 can be any suitablesize based on the overall size of the crank arm 100 and the expectedloading conditions, and can each be, for example, between about 2 mm andabout 15 mm or more, and/or between about 3 mm and about 10 mm. The neckportion 144 also defines a radial cross-sectional area measure in plane162.

Each extension 126 a also includes a retaining portion 166 that isconfigured to help lock the extensions 126 a within respective cavitiesformed in the carbon fibre body 102 and to help inhibit movement of theinsert 106 relative to the body 102, as explained in more detail below.The retaining portion 166 is a portion of the extension 126 a that isgenerally wider and/or deeper than the neck portion 144. The retainingportion 166 defines a retaining portion width 168, measured in a plane170 that is orthogonal to the radial direction 148 and is parallel toand radially outboard from the plane 162.

The retaining portion width 168 is selected to be larger than the neckportion width 160, and can be between about 3 mm to about 20 mm or more.The retaining portion 166 also defines a retaining portion depth 172(FIG. 3) measured in the insert axial direction. The retaining portiondepth 172 is selected to be larger than the neck portion depth 164, andcan be between about 3 mm to about 20 mm or more. The retaining portion166 also defines a retaining portion radial cross-sectional area,measured in plane 170, that is greater than the neck portioncross-sectional area. In this configuration, each extension 126 agenerally tapers from its retaining portion 166 to its neck portion 144.

In the illustrated example, the retaining portion 166 is provided at thetip 146 of the extension 126 a (i.e. is the radially outermost portionof the extension 126 a), such that the extension 126 a generally narrowsor tapers from the tip 146 to the neck portion 144. Alternatively, theextension 126 a may be configured such that the retaining portion 166(e.g. the portion with the largest radial cross-sectional area) ispositioned radially intermediate the neck portion 144 and the tip 146(for example if the extension were spherical).

Referring to FIG. 3, sidewalls 154 and 158 generally oppose each otherin the circumferential direction and are each inclined relative to theradial direction by a respective incline angle 174 and 176. Thesidewalls 154, 158 are inclined in such a manner that the extension 126a narrows in the circumferential direction from the retaining portion166 to the neck portion 144 and so that they generally converge towardthe insert axis 120. The incline angles 174 and 176 can be any suitableangle, including, for example between about 2 degrees and about 30degrees or more, and is preferably between about 7 degrees and about 15degrees. While illustrated as being generally equal, incline angles 174and 176 may be the same or different.

Referring to FIG. 4, sidewalls 152 and 156 generally opposed each otherin the insert axial direction. In the illustrated example sidewall 156is parallel to a plane 178 that is orthogonal to the insert axis 120whereas sidewall 152 is inclined at an angle 180 relative to the plane178. The angle 180 can be any suitable angle, and can be between about 2degrees and about 30 degrees or more, and is preferably between about 7degrees and about 15 degrees In this configuration, the extension 126 agenerally tapers from the retaining portion 166 to the neck portion 144in the insert axial direction, and the sidewalls 152 and 156 generallyconverge toward the plane 178. While illustrated with only one ofsidewalls 152 and 156 inclined, alternatively the extension 126 a can beconfigured so that both sidewalls 152 and 156 are inclined relative toplane 178, and converge toward the plane 178.

In the illustrated example, inclined sidewalls 152, 154 and 158 eachoverhang or overlie a portion of the radially outer surface 124 anddefine a respective cavity 182, 184 and 188 that can be filled with bodymaterial (e.g. carbon fibre material and epoxy resin) during the crankarm manufacturing process (explained in more detail below). This mayhelp anchor the extensions 126 a within the body 102. In contrast, inthe illustrated example, non-inclined sidewall 156 does not overhang theradially outer surface 124 of the insert base portion 122 and does notdefine a corresponding cavity.

While illustrated with two rings 130 and 136 of ten extensions 126 each,alternatively, the insert 126 a may include a different number of and/orconfiguration of extensions 126, and need not include two axially spacedapart rings 130 and 136 of extensions. The extensions 126 may beprovided in any suitable pattern or configuration, and may include onlya single set of extensions 126 and/or be configured so that eachextension extends substantially the entire axial length of the insert.

Referring to FIG. 8, in the illustrated example, the crank arm is formedby a molding process in which both the body 102 and insert 106 arecontained within a heated mold and held at elevated temperatures (forexample temperatures greater than 100 degrees Celsius). FIG. 8 is across-sectional view of a portion of the crank arm 100 while it is atthe elevated, molding temperature. Referring to FIG. 9, during thismolding process the carbon fibre body material is molded around theextensions 126 a thereby covering sidewalls 154 and 158 and is forcedinto the cavities 184 and 188 (illustrated as hatched areas in this FIG.9). Encasing the extensions 126 a in this manner may inhibit relativerotation of the insert 106 relative to the body 102.

Referring to FIG. 10, during the molding process the carbon fibre bodymaterial also encases sidewalls 152 and 156 and is forced into thecavity 182 (illustrated as hatched areas in FIG. 10). In the illustratedexample, the extensions 126 a are completed encased within the bodymaterial such that all of the sidewalls 152, 154, 156 and 158 arecovered by body material. Encasing the extensions 126 in this manner mayinhibit movement of the extensions 126 a, and therefore the insert 106,relative to the body 102 in insert axial direction.

After the molding process is complete, the molded crank arm is thenremoved from mold and cooled to room temperature. During the coolingphase the body 102 and the inserts 104 and 106 may shrink as a result ofthermal contraction.

FIGS. 5-7 illustrate the insert 106 and body 102 after the crank arm 100has cooled to room temperature. Referring to FIG. 5, in the currentexample, when the insert 106 is molded within the body 102 eachextension 126 is embedded within the body material and becomes encasedin a corresponding recess 190 formed in the body 102. The recesses 190are created as the body material is forced around the extensions 126during molding, and the shape of each recesses 190 generally matches theshape of its contained extension 126.

In the illustrated example, each recess includes four recess sidewallscorresponding to opposing extension sidewalls. Referring to FIG. 6,recess 190 a includes sidewalls 194 and 198 opposing extension sidewalls154 and 158 respectively. Referring to FIG. 7, recess 190 a alsoincludes sidewalls 192 and 196, opposing extension sidewalls 152 and 156respectively.

The recess 190 a also includes a recess end wall 200 overlying theextension end face 150, and defines an opening or throat region 204through which the neck portion 144 extends. The throat region 204surrounds the neck portion 144 and defines a throat width 206 measure inthe same plane 162 as the neck width 160 (FIG. 6) and a throat depth 208measured in the same direction as the neck depth 164 (FIG. 7). Thethroat width 206 is equal to or slightly greater than the neck width160, and the throat width 206 is less than the retaining portion width168. Similarly, in the illustrated example, the throat depth 208 isequal to or slightly greater than the neck depth 164 and is less thanthe retaining portion depth 172. In this configuration, the radialcross-sectional area of the throat (measured in plane 162) is equal toor greater than the cross-sectional area of the neck portion 144 and isless than the cross-sectional area of the retaining portion 166.

Referring to FIGS. 9 and 10, when the insert 106 and body 102 are bothat elevated temperatures during the molding process, each recess wall192, 194, 196 and 198 is in contact with its opposing extension sidewall152, 154, 156 and 158, and endwall 200 is in contact with end face 150.

As aluminium has a greater co-efficient of thermal expansion than carbonfiber, when the molded crank arm cools, the inserts 104 and 106 willtend to thermally contract or shrink more than the carbon fibre body102. When the extension 126 a cools it may tend to shrink radially.

Referring to FIGS. 6 and 7, in the illustrated example, the extension126 a shrinks by such an amount that the extension end face 150 becomesaxially spaced apart from the recess endwall 200 and a gap 202 iscreated. Absent a countering force, the presence of such a gap 202 maypermit the extension to move radially relative to the body resulting inloosening of the insert. However, in the illustrated example,corresponding shrinkage of the other extensions 126 a around theperimeter of the insert 106 create balancing forces that co-operate toinhibit movement of the insert 106 in the radial direction 148 relativeto the body 102.

Referring to FIG. 6, as the insert 106 shrinks the inclined orwedge-like configuration of extension sidewalls 154 and 158, andcorresponding recess sidewalls 194 and 198, allows the extensionsidewalls 154 and 158 to slide along the recess sidewalls 194 and 198.In this configuration, as the insert 106 shrinks the sidewalls 154 and158 do not lose contact with their respective recess sidewalls 194 and198. Instead, due to its tapered nature, the extension 126 a mayactually become more tightly seated within its cavity 190 a and thesidewalls 154 and 158 will be more tightly wedged against the recesssidewalls 194 and 198. This may allow the magnitude of the force actingbetween the extension sidewalls 154 and 158 and recess sidewalls 194 and198 to remain constant or increase as the insert 106 shrinks. Increasingthe force acting on the extension 126 a in the circumferential directionmay help hold the insert 106 firmly in place and may help inhibitrelative rotation of the insert 106 (about the insert axis 120) relativeto the body 102. While illustrated as a two-side wedge configuration(both sidewalls 154 and 158 are inclined) to help provide a balancedcircumferential wedging force, a similar wedging effect in thecircumferential direction may be achieved if only one of sidewalls 154and 158 is inclined.

Similarly, the wedge-like configuration of extension sidewall 152 andcorresponding recess sidewall 192 can provide a wedging or tighteningeffect in the insert axial direction as the insert shrinks 106.Providing such a wedge-like configuration in the axial direction mayhelp firmly hold the insert 106 in place axially, and may help preventtranslation of the insert 106 (along the insert axis 120) relative tothe body 102. In the illustrated example, the axial wedging features ofextensions 126 a in the first ring 130 are balanced by opposite axialwedging features of extensions 126 b in the second ring 136.

Due to the inclined configuration of sidewalls 152, 154 and 158 and thegenerally wedge-like nature of the extensions 126 the magnitude of theengagement forces holding the extensions 126 in place after they havecooled can exceed the magnitude of the surface friction between theextension sidewalls 152, 154 and 158 recess sidewalls 192, 194 and 198.

Increasing the reaction or engagement forces acting on the extensionsidewalls 152, 154 and 158 may increase the stress exerted on the neckportion 144 of the extension 126. Varying the inclination angle of thesidewalls 152, 154 and 158, the cross-sectional area of the neck portion144, the material of the insert 106 or any combination thereof may allowthe insert 106 to be configured to resist the elevated stress caused bythe expected thermal shrinkage.

The wedge-like configuration of the extensions 126 may also increaseengagement force between and extension 126 and its surrounding cavity190 may also increase when the insert is under load, for example whenthe crank arm is in use.

What has been described above has been intended to be illustrative ofthe invention and non-limiting and it will be understood by personsskilled in the art that other variants and modifications may be madewithout departing from the scope of the invention as defined in theclaims appended hereto.

The invention claimed is:
 1. A crank arm for a bicycle, the crank armcomprising: a body extending along a body axis and having a first bodyend and a second body end axially spaced apart from the first body end;an insert provided toward the first body end, the insert extending alongan insert axis, defining a radial direction orthogonal to the insertaxis and comprising a base portion, the base portion having a radiallyouter surface surrounding an axially extending aperture extendingthrough the base portion, the aperture configured to receive a fastenerfor connecting the crank arm to another component of the bicycle; atleast one extension disposed in a first ring of said extensions, saidextension extending outwardly from the radially outer surface, the atleast one extension encased within a corresponding recess in the body,said at least one extension encased within said corresponding recess insaid body restraining relative movement between the body and the atleast one extension about a direction along said insert axis, the atleast one extension comprising a neck adjacent the radially outersurface and a retaining portion spaced radially outward from the neck,the neck extending through a throat region of the corresponding recessand having a neck width measured in a first direction, the throat regionhaving a throat width measured in the first direction, the retainingportion having a retaining width measured in the first direction and theretaining width being greater than the throat width such that relativeradial movement between the at least one extension and the recess isinhibited and radial extraction of the at least one extension from thecorresponding recess is prevented; and a second ring comprised of atleast one extension, said second ring disposed proximate said first ringof said extensions.
 2. The crank arm of claim 1, wherein the body isformed from a body material having a first coefficient of thermalexpansion and the insert is formed from an insert material having asecond coefficient of thermal expansion, the second coefficient ofthermal expansion being greater than the first coefficient of thermalexpansion, and wherein shrinkage of the insert relative to the bodycannot radially extract the at least one extension from the cavity. 3.The crank arm of claim 2, wherein the extension further comprisesopposing first and second extension sidewalls spaced apart from eachother in the first direction, each extension sidewall extending betweenthe neck and the retaining portion, the first sidewall being planar andbeing inclined at a first angle relative to the radial direction so thatthe extension narrows from the retaining portion to the neck end towedge the extension within the recess to inhibit relative radialmovement therebetween.
 4. The crank arm of claim 3, wherein the recesscomprises a planar first recess wall inclined at the first anglerelative to the radial direction, the first extension sidewall opposingand bearing against the first recess wall whereby shrinkage of theinsert relative to the body increases the magnitude of a firstengagement force exerted between the first extension sidewall and thefirst recess wall to wedge the at least one extension more tightlywithin the recess in the first direction.
 5. The crank arm of claim 4,wherein the second extension sidewall is planar and is inclined at asecond angle relative to the radial direction, the first and secondextension sidewall being convergent toward the neck of the extension. 6.The crank arm of claim 5, wherein the first angle is equal in magnitudeto the second angle.
 7. The crank arm of claim 6, wherein the recesscomprises a planar second recess wall inclined at the second anglerelative to the radial direction, the second extension sidewall opposingand bearing against the second recess wall and wherein shrinkage of theinsert relative to the body increases the magnitude of a secondengagement force exerted between the second extension sidewall and thesecond recess wall.
 8. The crank arm of claim 1, wherein the neck has aneck depth measured in a direction parallel to the insert axis, theretaining portion has a retaining depth measured in the directionparallel to the insert axis and the throat has an throat depth measuredin the direction parallel to the insert axis, the throat depth beingequal to or greater than the neck depth and being less than theretaining depth.
 9. The crank arm of claim 8, wherein the extensionfurther comprises a third extension sidewall wall bounded by a firstextension sidewall, a second extension sidewall, the retaining portionand the neck, the third extension sidewall being planar and inclined ata third angle relative to the radial direction so that the extension istapered in the second direction between the retaining portion and theneck.
 10. The crank arm of claim 9, wherein the recess comprises aplanar third recess wall inclined at the third angle relative to theradial direction, the third extension sidewall opposing and bearingagainst the third recess wall whereby shrinkage of the insert relativeto the body increases the magnitude of a third engagement force exertedbetween the third extension sidewall and the third recess wall therebywedging the at least one extension more tightly within the recess in thesecond direction.
 11. The crank arm of claim 10, wherein the extensionfurther comprises a fourth extension sidewall spaced apart from thethird extension sidewall and bounded by the first and second extensionsidewalls, the retaining portion and the neck, the fourth extensionsidewall and the third extension sidewall being convergent toward theneck of the extension.
 12. The crank arm of claim 11, wherein the fourthsidewall is planar and extends in the radial direction.
 13. The crankarm of claim 1, wherein the at least one extension comprises a firstplurality of extensions circumferentially spaced apart from each otheraround a circumference of the radially outer surface of the insert. 14.The crank arm of claim 13, further comprising a second plurality ofextensions circumferentially spaced apart from each other around thecircumference of the radially outer surface of the insert and axiallyspaced apart from the first plurality of extensions along the insertaxis.
 15. The crank arm of claim 14, wherein each extension in thesecond plurality of extensions is opposite of a corresponding one of theextensions in the first plurality of extensions and is spaced apart fromthe corresponding one of the extensions in the first plurality ofextensions.
 16. The crank arm of claim 15, wherein the fourth extensionside wall of each extension in the first plurality of extension isopposite the fourth extension side wall of one corresponding extensionin the second plurality of extensions.
 17. The crank arm of claim 1,wherein the retention portion forms the radially outermost portion ofthe extension.
 18. The crank arm of claim 17, wherein the body is formedfrom a body material having a first coefficient of thermal expansion andthe insert is formed from an insert material having a second coefficientof thermal expansion, the second coefficient of thermal expansion beingdifferent than the first coefficient of thermal expansion and shrinkageof the insert relative to the body increases the magnitude of aretention force exerted between the body and the retaining portion ofeach insert.
 19. The crank arm of claim 1, further comprising: a secondinsert provided toward the second body end, the second insert extendingalong a second insert axis and defining a second radial directionorthogonal to the second insert axis, the second insert comprising asecond base portion having a second radially outer surface and at leastone second extension extending outwardly from the second radially outersurface, the at least one second extension encased within acorresponding second recess in the body, whereby relative planarmovement between the body and the at least one second extension isrestrained; the at least one second extension comprising a second neckadjacent the second radially outer surface and a second retainingportion spaced radially outward from the second neck, the second neckextending through a second throat region of the corresponding secondrecess, the second throat region having a second throat width, theretaining portion having a second retaining width, the second retainingwidth being greater than the second throat width to prevent radialextraction of the at least one second extension from the correspondingsecond recess.
 20. A crank arm for a bicycle, the crank arm comprising:a body having comprising a first end and a second end axially spacedapart from the first end along a body axis; an insert positioned withinthe body toward the first end, the insert extending along an insertaxis, defining a radial direction orthogonal to the insert axis theinsert comprising a base portion having a radially outer surface and aplurality of extensions extending outwardly from the radially outersurface, said plurality of extensions disposed in a first ring, eachextension encased within a corresponding recess in the body, saidextension encased within said corresponding recess in said bodyrestraining relative planar movement between the body and each extensionabout a direction along said insert axis; each extension comprising aneck adjacent the radially outer surface and a retaining portion spacedradially outward from the neck, each neck extending through a throatregion of one corresponding recess and having a neck cross-sectionalarea measured orthogonal to the radial direction, the throat having athroat cross-sectional area measured orthogonal to the radial directionand the retaining portion having a retaining cross-sectional areameasured orthogonal to the radial direction, the retainingcross-sectional area being greater than the neck portion cross-sectionalarea and the throat cross-sectional area such that radial extraction ofeach extension from the one corresponding recess is prevented; and asecond ring comprised of at least one extension, said second ringdisposed proximate said first ring.